ICDs for HCM

Abstract & Commentary

By John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco is a consultant for Novartis, and does research for Medtronic and Guidant.

Source: Maron BJ, et al. Implantable cardioverter-defibrillators and prevention of sudden cardiac death in hypertrophic cardiomyopathy. JAMA 2007;298(4):405-412.

This report describes a large group of patients with hypertrophic cardiomyopathy (HCM) who underwent implantable cardioverter defibrillator (ICD) implantation at 42 referral and nonreferral institutions in the United States, Europe and Australia. All HCM patients who received an ICD at participating institutions were followed in a registry and their outcome results are presented here.

The registry included 506 patients, who were aged 42 + 17 years at device implantation. One hundred and twenty-three patients received the devices for secondary prevention after episodes of ventricular tachycardia or cardiac arrest, while 383 patients thought to be at high risk received their ICD for primary prevention. The mean duration of follow-up was 3.7 years with a range of 1 to 16 years. Among the 506 study patients, 103 patients had one or more appropriate device terminations for either ventricular fibrillation (49) or ventricular tachycardia (54) during follow-up. The effective therapy was a defibrillation shock in 94 patients and overdrive pacing in 9, suggesting that most VT episodes were rapid with cycle lengths in the programmed ventricular fibrillation zone. The annual rate for appropriate interventions was 5.5% per year with a cumulative probability of appropriate intervention at 5 years of 23%. Among the 123 patients who had secondary prevention indications, 52 (42%) experienced appropriate ICD discharges during follow-up. This represented an appropriate intervention rate of 10.6% per year and a cumulative probability of appropriate discharge at 5 years of 39%. Among the 383 patients who received the device for primary prevention, 51 (13%) experienced an appropriate ICD discharge representing an annual intervention rate of 3.6% per year and a cumulative probability of discharge at 5 years of 17%.

Among the 103 patients with appropriate ICD therapies, 38 had a single appropriate intervention, 44 had 2 to 5 discharges, and 21 patients had more than 5 interventions. The time interval between ICD implant and the first appropriate discharge varied considerably and in 16 patients was between 5 and 10 years after insertion. The proportion whose first appropriate discharge occurred after 5 years was 27%. Age and gender did not affect the risk for appropriate ICD intervention and interventions were observed among patients taking all types of antiarrhythmic drugs. Of note, in the subgroup of patients who had interventions to relieve outflow tract obstruction, appropriate discharge rates were fourfold more common in patients with prior alcohol septal ablation (4 of 17, 24%) compared to patients who had previously undergone surgical septal myectomy (6 of 50, 12%). Combining various risk factors was not particularly helpful for grading prognosis is this group all of whom had at least one risk factor for sudden death. Twenty-four of the 173 (14%) patients with appropriate discharges had only one risk factor, 16 of 143 (11%) had 2 risk factors, and 10 of 59 (17%) had 3 or more risk factors. During the study period, 39 of 506 patients died and 10 underwent heart transplant. Nineteen of the 39 deaths were not directly related to their hypertrophic cardiomyopathy, but 20 died of either end-stage systolic dysfunction with advanced heart failure or embolic stroke. One final patient died with recurrent arrhythmia and an ICD malfunction.

Inappropriate shocks occurred in one-third of the patients; 132 patients who never received appropriate ICD intervention, as well as 34 patients who did receive an appropriate ICD intervention. Other major complications included infections (19 of 506, 3.8%), hemorrhage and thrombosis ( 8 of 506, 1.6%), and lead problems requiring intervention including fractures, dislodgement or oversensing (34 of the 506, 6.7%).

The authors conclude that an ICD effectively and reliably treats life-threatening ventricular arrhythmias in patients with hypertrophic cardiomyopathy. They believe their data argue that a single marker for high risk may justify consideration for a primary prevention ICD in patients with HCM.

Commentary

ICD insertion for the primary prevention of sudden cardiac death in patients with HCM remains a controversial topic. This report expands on earlier data from this multicenter registry and confirms that ICD therapy is an effective approach to sudden death prevention in patients with HCM. The problem of risk assessment for cardiologists who encounter patients with HCM in the office is still significant. As acknowledged by the authors, referral centers, such as those that participated in this registry, collect higher risk patients than those seen in community-based surveys of patients with HCM. Clearly, the ICD is the appropriate strategy for secondary prevention but the rate of appropriate ICD usage in the primary prevention group is lower yet these patients are at the same risk for complications, including inappropriate shocks, lead complications and infections. It is still appropriate to discuss these issues with patients and make sure they understand both the risks and benefits of ICD therapy before proceeding with implantation.